Many sensors, including fingerprint sensors, exist as part of a semiconductor die having micro-component transducers such as antennas. One popular fingerprint sensor is presented on a semiconductor die as an array of radio frequency (RF) antennas that receive low power transmissions directed to reflect from a user's finger presented above the array. One typical application of such a sensor, for example, is a laptop computer provided with a fingerprint sensor pad at one external surface. The laptop or other device may employ, mounted near an outer surface, a fingerprint scanner (or other biometric device), such as the “FingerLoc® 8600” (AFS8600) manufactured by AuthenTec. In such a case, the die may have a sensing area that comprises an RF fingerprint sensing array, which may be externally exposed as a sensor pad. The user presses a designated finger or thumb downward on the pad to identify themselves to the device and gain access.
Pressing a finger on a sensor pad often causes mechanical force to be applied to the sensor. In some cases, such force may overstress the structure of the sensor and package by, for example, bending the die or bending the package sufficiently to crack or break conductive layers within the package, causing electrical failure. Because the sensor pad is presented at an exposed surface, it may be subjected to other forces such as being struck or squeezed by common scenarios like the device being hand-carried, dropped, or having object stacked on top of it.
Some previous sensor packages provide compressible material beneath the sensor array to help absorb such forces. However, such schemes typically suffer from a variety of problems. One problem is that a semiconductor die containing the sensor or sensor array may be bent by the stress and may fail or crack as a result. Another problem is that downward forces may cause the sensor die to peel away from the flexible circuit to which it is mounted. Still further, the forces applied to the sensor array may cause mechanical stress and failure at other parts of the sensor package, such as conductive traces, or output connection contacts, for example.
What is needed are semiconductor circuit modules or packages that enable semiconductor die or other sensor transducers to be presented along an outer surface of the package while still absorbing forces applied to the sensor sufficiently to prevent failure.